Arc heater having means for varying and adjusting the cross sectional area of the passageway through which the gas to be heated flows



Feb. 24, 1970 Y J. B. HAMMER 3,497,765

ARC HEATER HAVING MEANS FOR VARYING AND ADJUSTING THE CROSS SECTIONAL AREA OF THE PASSAGEWAY THROUGH WHICH THE GAS TO BE HEATED FLOWS Filed Aug. 2, 1967 2 Sheets-Sheet 1 FIG. 5.

LENGTH PARAMETER, I/W ms lkg Feb. 24, 1970 J. B. HAMMER 3,497,765

ARC HEATER HAVING MEANS FOR VARYING AND ADJUSTING THE CROSS SECTIONAL AREA OF THE PASSAGEWAY THROUGH WHICH THE GAS TO BE HEATED FLOWS 2 Sheets-Sheet 2 Filed Aug. 2, 1967 2 FIG. 3.

3,497,765 ARC HEATER HAVING MEANS FOR VARYING TAND ADJUSTING THE CROSS SECTIONAL AREA OF THE PASSAGEWAY THROUGH WHICH THE GAS TO BE HEATED FLOWS Joel B. Hammer, Pittsburgh, Pa., assiguor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Aug. 2, 1967, Ser. No. 657,807 Int. Cl. H01j 7/24, 17/26; Hb 31/26 US. Cl. 315111 14 Claims ABSTRACT OF THE DISCLOSURE A gas arc heater apparatus having a gas flow passageway defined by spaced walls at least one of which is movable with respect to the others to vary the cross-sectional area of the gas flow passageway to provide increased eflicieilcy of electric power consumed imparts a desired enthalpy to the gas being heated with a minimum of arc current and optimum cross-sectional area of the gas flow passageway.

Background of the invention This invention relates to improvements in arc heaters and more particularly to an arc heater having a gas flow passageway of adjustable cross-sectionalarea to thereby control and maximize the efficiency of the arc heater when the arc heater is operating over a range of conditions.

Generally speaking, prior art are heaters which must operate over a range of conditions pay a severe penalty, with a resulting inefficiency, by having a non-optimum flow area for some of the conditions of operation. Since fixed flow area heaters are sized for the highest Mach number condition, lower Mach number operation occurs with excessive area, and excessive arc current is required to produce a designed enthalpy.

My invention overcomes the disadvantages and limita tions of the prior art by providing fluid cooled walls at least one of which may be moved with respect to the others to provide a gas flow passageway, the cross-section of -which may be varied and adjusted at will in accordance with the speed of movement of the gas and other operating conditions.

Summary of the invention.

In summary, in one embodiment of my invention, I provide two parallel stationary preferably fluid cooled walls and two walls intermediate the parallel stationary walls at least one of which may be moved toward the other or away from the other in a translatory movement to". adjust the cross-sectional area of a gas flow passage therebetween.

' In another embodiment I provide an arc heater with a gas flow passageway having four walls, all of which are movable with respect to each other, so that the shape of the gas flow passageway may be maintained uniform, if desired, while the cross-sectional area is varied.

Accordingly, a primary object of the invention is to provide a new and improved arc heater.

Another object of the invention is to provide a new and improved arc heater having a gas flow passageway of vari able cross-sectional area.

Another object is to provide a new and improved gas are heater in which the efliciency of the arc heater may be maintained near maximum by adjusting the cross-sectional gas flow area with variations in the speed of movement of the gas through the arc discharge path.

Brief description of the drawings FIGS. 1 and 2 are perspective views of the Walls forming the gas flow passageway according to one embodiment nited States Patent Patented Feb. 24, 1970 of my invention, showing how the walls are moved with respect to each other to adjust the cross-sectional area of Description of the preferred embodiments Referring now to the drawings, in which like reference numerals are used throughout to designate like parts for a more detailed understanding of the invention, and in particular, to FIGS. 1 and 2, the gas flow passageway is seen to be formed by four elongated wall sections 11, 12, 13 and 14 which, as will become more clearly apparent, are preferably fluid cooled, and which are generally semirectangular in cross-section, providing a gas flow passageway 15 of the cross-sectional area shown. In FIG. 2, the same wall sections 11, 12, 13 and 14 have been moved in a manner to reduce the cross-sectional area of the gas flow passageway 15'.

Particular reference is made now to FIG. 3, a view through a complete arc heater including a pressure vessel. The pressure vessel generally designated 21 has a bore or opening 22 therethrough at one end 24 in which is disposed gas inlet means 23. A larger bore or opening 25 is seen in Wall 26, the bore 25 having mounted therein a nozzle member 27 with an exhaust passageway 28. Near the aforementioned wall 24 and separated therefrom by la heat resistant insulating ring 30 is a first electrode 31 having lead means 32 connected thereto for connecting the electrode 31 to one terminal of a source of potential for producing and sustaining the are 47. Lead 32 includes a variable resistor 34 symbolizing means for adjusting the arc current. It will be understood that the lead 32 passes through an insulating bushing in the pressure vessel 21, the insulating bushing not being shown for simplicity of illustration.

At the other extremity of the chamber 33 formed inside the pressure vessel 21, and preferably coaxially aligned with the aforementioned nozzle member 27, is an insulating ring 41 which spaces the second electrode 42 from the pressure vessel and electrically insulates it therefrom. Electrode 42 has lead means 43 which it is understood is connected to the other terminal of the aforementioned source of potential, and which passes through a bushing of electrically insulating material in the pressure vessel the last-named bushing not being shown for simuplicity of illustration. The aforementioned wall portions of the equipment which determine the size of the gas passageway are electrically insulated from the electrodes 31 and 42 by insulating ring members 45 and 46. The are 47 is seen taking place through the passageway 48 between the aforementioned electrodes 31 and 42. It is seen in FIG. 3 that each of the semi-rectangular wall sections with its three sidesds made up of a plurality of individual U- shaped or semi-rectangular members composed of metal and having fluid passageways therethrough, the individual members of each wall section being electrically insulated from the adjacent members on each side thereof. One of these fluid flow passageways is shown in dashed-line in FIG. 4 and is designated 50. It is seen to communicate at each end thereof with a fluid inlet header and a fluid outlet header, the particular fluid inlet header being desig nated 51 and the fluid outlet header 52. The relative posi tions of the fluid inlet header and the fluid outlet header could be reversed, if desired. The headers extend substantially the entire length of the wall section or wall portion and have a plurality of conduits 53 and a plurality of conduits 54 connecting them to the passageways in the members of the wall section as well as inlet pipe mean 55 and outlet pipe means 56.

Referring more particularly again to FIG. 3, a sectional view is shown through the wall portion 61 of FIG. 4, the other wall portions of FIG. 4 being generally designated 62, 63 and 64. Wall portion 61 is seen to include 16 members, FIG. 3, these being designated 7186 inclusive, the members being electrically insulated from each other by insulating members and also electrically insulated from clamping members 91 and 92, the insulating members being designated 88, there being 17 insulating members in all. The insulating members 88 are, in fact, shaped similar to the cross-sectional shape of the various wall sections or portions. The wall members 71-86 are seen to have individual fluid flow passageways there through, these passageways being shown at 94. Each of the passageways 94 is connected by conduit means to a fluid header 95, one of the conduit means being shown at 96, FIG. 4. And as seen in FIG. 3, the fluid header 95 has a fluid inlet or outlet pipe 97 connected thereto, fluid inlet or outlet pipe 97 threadedly engaging a coupling member 98 passing through a bore 99 in wall 26, the coupling mem ber 98 being connected with a further fluid conduit 100 external to the pressure vessel.

The aforementioned fluid flow passageways 94 in the members of wall section 61 communicate at the other ends thereof by way of a plurality of conduits 101 with the fluid header 102, not shown in FIG. 3, which is connected to a fluid inlet or outlet pipe 103, not shown in FIG. 3 which it is understood passes through the wall of the pressure vessel.

Referring again particularly to FIG. 4, it is seen that the wall section 61 has a bar or rod 105 extending along the length thereof to which is attached an arm 106 pass ing through an electrically insulating bushing member 107 in wall portion 108 of the pressure vessel. The arm 106 is slidable in a bore 109 which passes through the bushing 107 and the wall 108 at substantially a 45 angle thereto. As seen in FIG. 4, the other wall sections 62, 63 and 64 have bars 112, 113 and 114 connected thereto along the length thereof to which are connected lever arms 122, 123 and 124 respectively, all of which contain bends of substantially 45 so that they pass through the walls of the pressure vessel at substantially a 45 angle with respect to the plane of the wall. Lever arm 123 is shown passing through a bore 125 in bushing 126 mounted in wall portion 127.

As will be readily understood by those skilled in the art, in restricting or enlarging the cross-section of the gas flow passageway 48, it is most convenient to move the wall sections 61-64, inclusive, in these particular angular directions so that the cross-section of the gas flow pas= sageway 48 remains substantially square.

Particular reference is made again to FIG. 3. in accordance with the section line IIIIII of FIG. 4, the discrete members which make up the wall section generally designated 64 are seen in portions thereof, these portions being designated 141456, inclusive, and it is seen that the wall members are connected by conduits 158 individually with a fluid header 159 having a fluid inlet or outlet pipe 160 connected thereto. The wall members 141-156 are electrically insulated from each other by in sulating members 163 which are generally shaped to conform to the cross-section of the wall sections, and the wall members are also electrically insulated from. clamping portions 165 and 166, there being 17 insulating members in all.

Particular reference is made now to FIG. 4, where it is seen that the wall section 64 also has a fluid inlet or outlet header 167 with conduits 168 and 169, and that the aforementioned wall section generally designated 62, not shown in FIG. 3, has a fluid inlet or outlet header 171 with conduits 172 and 173 and, at the other extremity 4 thereof, has a fluid inlet or outlet header 176 with con duits 177 and 178.

Particular reference is made now to FIG. 6, a graph illustrating the operation of the apparatus of FIGS. 3 and 4. The curve represents the enthalpy parameter as a function of the length parameter. The cross-sectional area of the gas flow passageway is related to d, the constrictor diameter. The term constrictor diameter may be thought of as synonymous with gas passageway diameter. In the enthalpy parameter, H is the total enthalpy, d is the constrictor diameter, I is the arc current, these being measured in units where l is joules, m. is meters, kg. is kilograms and a. is amperes. The horizontal coordinate, or the length parameter, is shown where l is the length of the constrictor, w is the mass flow rate through the constrictor, and the units include s in seconds.

Using FIG. 6 it can be seen that for a given length of heater, 1 and given mass flow, w, the enthalpy parameter Hd/ 21 is essentially fixed. For a desired value of H one can achieve this value of Hd/ZI by varying either d or I or both. Since variation of 1 effects the consumed power and consequently the heater efficiency it is more desirable to select the minimum suitable Iand vary d. Variationin d is essentially a variation in flow area, A. For the purpose of understanding this invention it may be better to con= sider variation of d as a variation of A.

On the graph all open symbols have the same nozzle throat size, 0.635 centimeter in diameter. All solid symbols represent a nozzle throat 1.27 centimeters in diameter. Some of the open symbols were obtained with different are heaters, and they still show the same correlation indicating that the effect described and claimed herein is not re stricted to one are heater.

The size of the channel has a practical lower limit for most applications. This limit is set by a Mach number at which M is substantially equal to or less than 1. For gas flows greater than that required for M=1, the gas pressure goes up rapidly, thereby increasing losses of energy and total pressure. Consequently, it is more efficient to operate with Mach substantially equal to less than 1. To show that it is ineflicient to operate at low Mach numbers of the order of 0.1 to 0.01, that is, operate with excessive flow area, reference may be had to a work by H. A. Stine, V. R. Watson, and C. E. Shepard entitled Effect of Axial Flow on the Behavior of a Wall-Constricted Are, a paper presented to the AGARD Specialists meeting on are heaters and MHD accelerators for areodynamic purposes, at Rhode-Saint-Genese, Belgium, Sept. 2l-23, 1964, thought to be in a group of papers published by the National Aeronautics and Space Adminis tration, further identified as TEE-X54065, dated Septem ber, 1964. In that paper it is shown that for a round tube:

Hd Z n where H is the total enthalpy, in joules per kilogram.

I is the arc current (in ampercs) e is a symbol indicating that one quantity is a function of the other.

1 is the length of the constrictor passageway (in meters).

m w=rnass flow rate of gas through the constrictor pas-- sageway (in kilograms per second).

Stine and Watson further show that:

for a given length, where d=constrictor diameter (in meters). A=I=are current (in amperes).

Stine and Watson still further show that:

where A is the cross-sectional area of the flow area of the constrictor, and the other terms are measured in the same units as before.

For a given length, l, and mass flow, iv (in), the term in brackets is fixed and:

where C represents the value of /?X evaluated at given values of l and m. It further follows that:

For any given output enthalpy I-l it follows that:

I =C /Z P==power V=arc voltage I=arc current C =C V evaluated at the operating voltage.

For example, the consequences of the last equation show that if an arc heater is operated at four times the required 'ar ea (two times the desired diameter or two times the side length for a square or rectangular flow area) the arc heater consumes two times the power for a given end product. Where arc heaters operate over a wide range of conditions, a severe penalty in excess power may be paid. It is not uncommon for gas flow areas to be ten times larger than necessary. In arc heaters used for chemical processing, it is particularly necessary that eflicient arc operation be achieved if eflicient chemical conversion is to be obtained.

All of the above equations are exemplary and are not limiting. Actual arc heater behavior may be somewhat different from the foregoing mathematical explanation, without invalidating my end conclusions or the novelty which I claim for my invention.

By Way of summary I claim as my invention a variable flow arc heater which allows substantial increase in efliciency by allowing operation at optimum gas flow area for more than one operating condition. I further have invented new and novel means of achieving variable area operation for the gas flow in an arc heater.

As previously stated in FIGS. 3 and 4, the net direction of motion of each wall is 45 to the wall surface. The desired movement could be supplied by providing for translating motion of the actuator in two planes to thereby provide the desired direction of wall movement.

In the embodiment shown in FIGS. 3 and 4, the position actuators or arms 106, 122, 1 23 and 124 extending through the'walls of the pressure vessel supply the main supporting means for the walls which provide the gas flow restricting passageway. The invention contemplates and includes the use of additional means, now shown, for supporting the walls which provide the gas flow restricting passageway.

Instead .Qf flexible hoses being attached to the inlet and outlets, stiff actuators could conduct fluid and at the same time move the walls which provide the gas flow restricting passage, if desired.

Additional papers which may be referred to for a mathematical treatment of certain principles which may be made use of in apparatus embodying my invention include the following: H. A. Stine and V. R. Watson,

entitled The Theoretical Enthalpy Distribution of Air in Steady Flow Along the Axis of a Direct-Current Electrio Arc, NACA D4331, August 1962; J. R. Jedlicka and H. A. Stine, entitled Axial Flow Through the Wall Constricted Direct-Current Arc-Comparison of Theory and Experiment, a paper delivered at the International Symposium on Plasma Phenomena and Measurements, sponsored by the IEEE, San Diego, Calif., Oct. 29, 196-3.

My invention includes a variable area gas flow passage defining means in which only one wall is moved to charge the cross-sectional area, for example, the upper wall of FIG. 5.

My invention includes a structure in which small electrodes are disposed Within the walls which define the crosssectional area of the gas flow passageway, the walls serv= ing as part or all of a pressure vessel.

The above written description and the drawings attached hereto are illustrative only and are not to be interpreted in a limiting sense.

I claim as my invention:

1. In an arc heater including means forming an arc chamber, gas inlet means for introducing gas to be heated, exhaust means, a first electrode and a second electrode disposed in spaced positions and electrically insulated from each other, and means for connecting the first and second electrodes to a source of potential to supply an arc current and produce an arc therebetween, the improvement which comprises gas flow passage defining means interposed between the first electrode and the second electrode, the arc between electrodes extending throiigh the passage formed by said gas flow passage defining means, the gas flow passage defining means consisting of four semi-rectangular Wall portions at least two of'which are movable to change the cross-sectional area of the gas flow passage, and moving means operatively connected to the movable wall portions for changing the positions of the wall portions to thereby change the cross-sectional area of the gas flow passage.

2. Arc heater apparatus according to claim 1 including in addition means for varying the current which produces the arc.

3. Arc heater apparatus according to claim 1 in which all of the wall portions are additionally characterized as being fluid cooled.

4. An arc heater according to claim 1 in whichthe moving means includes means operatively connected to each of the four semi-rectangular wall portions for moving the wall portions at an angle of substantially 45 with respect to the longitudinal axis of the portion to thereby vary the cross-sectional area of the gas flow passageway while maintaining the shape of the gas flow passageway substantially unchanged.

5. A gas are heater according to claim 1 in which each of the semi-rectangular wall portions forming the gas flow passageway is additionally characterized as being composed of a number of stacked, adjacent, discrete wall members, each of the members being electrically insulated from the adjoining members on both sides thereof, each of the members having a fluid flow passageway therein extending substantially all the way therearound.

6. Arc heater apparatus according to claim 5 including in addition fluid inlet header means individually connected to the fluid flow passage in each of the members at one end of the fluid flow passageway, and including in addition fluid outlet header means individually connected to the fluid flow passageway in each of the members at the other end thereof.

7. Are heater apparatus according to claim 5 including in addition clamping means disposed at the ends of the stacked, discrete wall members for clamping the wall members together.

8. Arc heater apparatus according to claim 4 including in addition a pressure vessel, and the moving means includes four movable arms operatively connected to the four semi-rectangular wall portions defining the gas flow passageway, the four movable arms extending through the walls of the pressure vessel and being adapted to be manipulated from outside the pressure vessel to change the relative positions of the semi-rectangular wall portions and thereby vary the cross-sectional area of the gas flow passage,

9, In an arc heater including means forming an arc chamber, gas inlet means for introducing gas to be heated, exhaust means, first and second electrodes mounted in spaced positions and electrically insulated from each other, and means for connecting the first and second electrodes to a source of potential to supply an arc current and produce an arc therebetween, the improvement which comprises gas flow passage defining means interposed between the first electrode and the second electrode over at least the major portion of the arc length, the passage defining means forming a passageway of adjustable cross-section but of substantially uniform crosssectional area over the entire length thereof, the arc between electrodes extending through the passageway formed by said gas flow passage defining means, and means operatively connected to the passage defining means for changing the cross-sectional area in a uniform manner over substantially the entire length thereof.

10. An arc heater according to claim 9 wherein the passage defining means includes means forming four rec-= tangular surfaces extending in planes parallel to the longitudinal axis of the arc heater and enclosing a space rectangular in cross-section with a cross-sectional area adjustable by moving at least one of the rectangular sur faces, and the means for changing the cross-sectional area includes moving means operatively connected to said lastnamed rectangular surface for altering the position of the last-named surface without moving the last-named surface out of a plane parallel to the longitudinal axis of the arc heater.

11, An arc heater according to claim 10 wherein the means forming four rectangular surfaces each consists of a plurality of discrete aligned segments, each segment being electrically insulated from adjacent segments on both sides thereof to inhibit the are from striking to the wall of passage defining means.

12, 'An arc heater according to claim 11 wherein each segment has a passageway therethrough for the flow of cooling fluid, and including in addition fluid inlet header means and fiuid outlet header means communicating with the passageways for the flow of cooling fluid.

13, An arc heater according to claim 10 wherein two of the rectangular surface forming means are movable, and the moving means is operatively connected to both said two surface forming means,

14., In an arc heater, having a pair of electrodes spaced from each other a predetermined distance and electrical circuit means adapted to electrically connect the electrodes to terminals of opposite polarity respectively of a source of potential to produce and sustain an are therebetween, the arc heater having an exhaust vent and being adapted to have gas to be heated admitted thereto at an adjustable rate, means forming a gas flow and. are constrictor passageway of adjustable but uniform diameter and cross-sectional area over the entire length thereof, the passageway forming means extending over at least the major portion of the arc length, said length being predetermined thereby providing a predetermined length parameter which determines the value of an enthalpy parameter, where the length parameter is equal. to 1/ w,

where 1 is measured iii meters and w is the mass flow rate of gas through the constrictor passageway measured in kilograms per second, the enthalpy parameter Hd/ZI being a. function of the length parameter, where d is the diame ter of the constrictor passageway in. meters and I is the arc current in amperes, the cross-sectional area of the constrictor passageway being a function of the diameter, means operatively connected to the constrictor passageway forming means for adjusting the diameter thereof to thereby adjust the cross-sectional area, and means in the electrical circuit for adjusting the value of the are current, the diameter and thereby the cross-section of the constrictor passageway being adjusted for maximum efiiciency to a value whereat a minimum value of I satisfies the term. d/2I for the value of the enthalpy parameter and the desired magnitude of enthalpy H. in. joules per kilogram,

References Cited UNITED STATES PATENTS 1/ 1967 Prattetal 3]3231 l/1968 Stine et al 2l912l UIS, CL X.R. 2l9--121; 313-231 

